1. Field of the Invention
The invention relates to obtaining an optical lens from a polymerizable material, in particular, although not exclusively, an ophthalmic lens.
2. Description of the Related Art
It is known that it is possible to obtain a lens of this kind with a mold formed of two shells disposed at a distance from and facing each other and an annular seal cooperating with the periphery of the shells to define a molding cavity. The faces of the shells facing toward the cavity are generally concave and convex, respectively, and have a shape corresponding to the anterior face and the posterior face, respectively, of the lens to be obtained, in order for the anterior and posterior faces to have the required shape upon removal from the mold or after machining to finish them.
Diverse methods of obtaining an optical lens with a mold of this kind are known already, and in particular a method in which the first step is to place the molding shells on the seal, a spring clamp for retaining the shells is then fitted, the cavity is then filled manually using an injection nozzle that is inserted between the seal and one of the shells thanks to deformation of the seal and slight movement of the shell in question against the action of the clamp, filling continuing until overflowing occurs, in order to expel excess air, and the filled mold held in the assembled state by the clamp is then transported to a water bath in which the material introduced into the mold is polymerized by heat.
To enable the mold to accompany shrinkage of the material that it contains during polymerization, the seal is adapted to be compressed axially by the effect of the movement of the shells toward each other caused by the shrinkage.
There have already been proposed, in particular in U.S. Pat. No. 3,136,000 and in international application WO 00/30836, molds of the kind mentioned above in which the seal has respectively one lateral hole and several lateral holes, the polymerizable material being introduced into the cavity of the mold by means of a nozzle fitted into the filling hole in the manner of a syringe, the air initially present in the molding cavity escaping respectively via a passage separate from the nozzle and via at least one vent hole separate from the filling hole. After introduction of the polymerizable material into the mold, the single hole and the multiple holes are respectively plugged by a flap that returns to a position in front of the single hole during the removal of the nozzle and by plugs that are pushed into the multiple holes from the outside.
There has also been proposed, in particular in U.S. Pat. No. 4,251,474, for situations in which there is no hole in the seal, to dispose the mold horizontally, to introduce the filling nozzle between the seal and the upper shell and then, once the mold has been filled and the nozzle removed, to move the upper shell downward by means of an external mechanical force while bracing the lower shell, so that the excess portion of the material introduced into the mold gets past the lip of the seal cooperating with the upper shell and overflows out of the mold. When the upper shell is released, the seal tends to return to its original configuration, but because air is not able to penetrate into the molding cavity, each molding shell is held in contact with the seal in the manner of a sucker, so that there is no need to use the spring clamp referred to above, which could anyway provide only a modest spring force compared to the forces that may be produced mechanically.